The use of mobile communications networks has increased over the last decade. Operators of mobile communications networks have increased the number of base stations in order to meet an increased request for service by users of the mobile communications network. The base stations typically comprise radio systems for relaying radio signals. The radio signals are typically relayed into and from a cell of the mobile communications network, and vice versa. It is of interest for the operator of the mobile communications network to reduce the running costs of the base stations. It is one option to implement the radio system as an antenna embedded radio system. With the antenna embedded radio system some of the hardware components of the radio system may be implemented on a chip. The antenna embedded radio system therefore reduces the costs of the base station. Implementing the radio system as the antenna embedded radio system reduces space needed to house the hardware components of the base station. Power consumption during normal operation of the radio system is substantially reduced when implementing the antenna embedded radio system comprising the chip.
It is of interest to provide a reliable quality of service to an individual user of the mobile communications network given the increase in the number of users. Several techniques have been suggested in order to deal with the increased number of users within the mobile communications network. One of the several techniques comprises beam forming capabilities in order to direct a beam relayed by the radio system in different directions to improve service coverage within the cells of the mobile communications network. The beam forming techniques rely on defined phase and amplitude relations between several of the antenna elements of the active antenna system. A transmit path and/or a receive path is associated with each antenna element. Calibration of the transmit paths and the receive paths is required to provide the defined phase and amplitude relationship between the beams. The calibration allows the estimation of a phase and amplitude deviation accumulated along the transmit path of the radio system. Likewise the calibration comprises estimating phase and amplitude deviations accumulated along the receive paths of the radio system. The calibration may further comprise a determination of transit times needed for a message signal to travel from a digital radio interface to the antenna element in order to be relayed. In a second step the phase and amplitude deviation accumulated along the transmit paths can be corrected. An appropriate phase and amplitude change may be applied to the individual transmit/receive paths to yield the defined phase and amplitude relationship between the individual transmit/receive paths of the radio system, in order to allow for beam forming techniques.
In a modern mobile communications network a payload signal is provided as a packetized payload signal to the radio system. Packets of the packetized payload signal have a defined temporal order when the packetized payload signal is provided to the digital radio interface. Within the radio system some processing may be applied to the packetized payload signal. The processing typically comprises the packetized payload signal passing several buffers and phase locked loops (PLLs). With the data processing the defined temporal order of the packets may be deteriorated or even destroyed. In the prior art, with non-packetized signals, it was possible and common practise to calibrate transmit paths along which the non-packetized payload signal travels when being relayed by the radio station upon manufacture of the radio system. The relaying by the radio station comprises the data processing.
The present invention is combinable with a digital predistortion system as known in the art. A co-pending application of the applicant U.S. Ser. No. 12/416,596 discloses the calibration of phase and amplitude changes and the updating of a digital predistortion in the case of non-packetized internal radio signals. The teachings of U.S. Ser. No. 12/416,596 are incorporated herein by reference. A further co-pending application of the applicant U.S. Ser. No. 12/416,626 discloses the calibration of phase and amplitude changes and the updating of a digital predistortion in the case of a packetized internal radio signals.
Radio systems are critical to a transit time from a radio signal reaching the digital radio interface until a corresponding radio signal is relayed by antenna elements of the radio system. The transit time is affected by any change in cable length and the like.
In the prior art it was necessary to recalibrate the radio system whenever a component of the radio system, for example, a cable, was replaced. Furthermore there was only very little flexibility with respect to a spatial arrangement of the transmit paths and/or the antenna elements of the prior art radio system. The recalibration in the prior art is expensive and time consuming.
U.S. Pat. No. 6,693,588 B1 (assigned to Siemens) discloses an electronically phase-controlled group antenna. The electronically phase-controlled group antenna is calibrated using a reference point shared by all the reference signals. In the downlink, reference signals which can be distinguished from one another are simultaneously transmitted by individual antenna elements of the group antenna and are suitably separated after reception at the shared reference point.
The Siemens system requires a fixed spatial arrangement of the antenna elements.